NI WSN-3214 User Guide and Specifications
18
ni.com
•
V
r
—Offset compensated ratiometric bridge output defined by the following equation.
•
V
CH
—Measured voltage of the bridge:
Note
The ratio of the bridge output voltage to the excitation voltage is calculated internally on the
NI WSN-3214. Shunt Calibration is only supported for quarter-bridge. If you are switching from
using a quarter-bridge to a half-bridge or full-bridge configuration, you need to specify 1 for Shunt
Calibration, and then perform Offset Null in the software.
The NI WSN-3214 converts the readings to strain using the following equation:
To compensate for lead resistance errors shunt calibration should be used. For more information, refer
to the
section.
Half-Bridge Type I
This section provides information for the half-bridge strain-gage configuration type I. The half-bridge
type I measures either axial or bending strain. Figure 15 shows how to position strain-gage resistors in
an axial and bending configurations. Figure 16 shows the half-bridge type I circuit wiring diagram.
Figure 15.
Half-Bridge Type I Measuring Axial and Bending Strain
A half-bridge type I has the following characteristics:
•
Two active strain-gage elements. One strain-gage element is mounted in the direction of axial strain
while the other acts as a Poisson gage and is mounted perpendicular to the principal axis of strain.
•
Half-bridge completion resistors (R
1
and R
2
) are provided by the NI WSN-3214.
•
Sensitive to both axial and bending strain.
•
Sensitivity ~ 0.5
μ
V/V per
με
, for GF = 2.0,
ν
= 0.
Vr
VCH
VEX
------------
Shunt Calibration
×
Offset Null
–
=
strain
ε
( )
4
Vr
–
GF
1 2
Vr
+
(
)
--------------------------------
=
(– )
R
4
(+ )
(– )
Axi
a
l
Bending
R
3
R
3
R
4
(+ )
